A 60-year-old patient presents with extensive bullae, target-shaped lesions surrounded by erythema, and genital involvement. What is the most likely diagnosis?

Explanation

The presence of widespread bullae, target lesions with erythematous halos, and genital lesions strongly indicates Stevens-Johnson syndrome. Herpes zoster typically presents with painful vesicular rash in a dermatomal distribution, herpes simplex often causes localized vesicles without target lesions, and herpangina is characterized by oral ulcers without bullae or target lesions.